DE102007056627A1 - Method for simultaneously grinding a plurality of semiconductor wafers - Google Patents

Abstract

The invention relates to a method for simultaneous double-sided grinding a plurality of semiconductor wafers, each wafer is freely movable in a recess of a plurality of offset by means of a rolling device rotors and is thereby moved on a cycloidal trajectory, wherein the semiconductor wafers between two rotating annular working disc material each work disc comprises a working layer containing bonded abrasive, characterized in that the shape of the working gap formed between the working layers during grinding is determined and the shape of the working surface of at least one working disk mechanically or thermally depending on the measured geometry of the working gap is changed so that the working gap has a predetermined shape. The subject matter of the invention is also a method in which the semiconductor wafers temporarily leave the working gap with part of their surface during processing. The invention also relates to a method in which the carrier disc is made entirely of a first material or a second material of the carrier disc is completely or partially coated with a first material such that during grinding only the first material is in mechanical contact with the working layer and the first material does not change the sharpness of the abrasive ...

Description

object The present invention is a method for simultaneous double-sided grinding of multiple wafers, each wafer freely movable in a recess of one of several by means of a Rolling device in rotation offset carriers and thereby moved on a cycloidal trajectory, wherein the semiconductor wafers between two rotating annular Working discs are machined material removing, with each Working disk includes a working layer, the bonded abrasive contains.

State of the art

For Electronics, microelectronics and micro-electromechanics are called Starting materials (substrates) Semiconductor wafers with extreme Requirements for global and local evenness, front-sided local flatness (nanotopology), roughness, cleanliness and freedom of foreign atoms, in particular metals. Semiconductor wafers are slices of semiconductor materials. Semiconductor materials are Compound semiconductors such as gallium arsenide or elemental semiconductors such as mainly silicon and occasionally germanium or also layer structures of the same. Layer structures are for example a component-bearing silicon top layer on an insulating intermediate layer ("Silicon on insulator", SOI) or a lattice-tense Silicon top layer on a silicon / germanium intermediate layer with towards the top layer increasing germanium content on a silicon substrate ("Strained silicon", s-Si) or combinations of both ("Strained silicon an insulator", sSOI) are preferred in single-crystalline form for electronic components or in polycrystalline form preferred for solar cells (Photovoltaic) used.

• a) mechanische Bearbeitung;
• b) chemische Bearbeitung;
• c) chemo-mechanische Bearbeitung;
• d) ggf. Herstellung von Schichtstrukturen.

In order to produce the semiconductor wafers, a semiconductor rod is produced according to the prior art, which is first separated into thin slices, usually by means of a wire-saw (MWS), followed by one or more processing steps, which generally take place in the following groups to divide:

• a) mechanical processing;
• b) chemical processing;
• c) chemo-mechanical processing;
• d) if necessary, production of layered structures.

The Combination of the individual steps attributable to the groups as well as their order varies depending on the purpose. Further comes a variety of secondary steps such as edge processing, cleaning, sorting, Measuring, thermal treatment, packaging, etc. are used.

mechanical Processing steps according to the prior art are lapping (simultaneous double side lapping a plurality of semiconductor wafers in the "batch"), the Single-side grinding of individual semiconductor wafers with one-sided Clamping of the workpieces (usually as sequential double side grinding carried out; "Single-side grinding", SSG; "sequential SSG ") or the simultaneous double-side grinding of individual semiconductor wafers between two grinding wheels (simultaneous "double-disk grinding ", DDG).

The chemical processing includes etching steps such as alkaline, acidic or combination etching in the bath, possibly with movement of semiconductor wafers and etching bath ("laminar-flow etch ", LFE), one-sided etching by the application of etchant in the center of the disc and radial centrifuging by disc rotation ("Spin etch") or etching in the gas phase.

The Chemo-mechanical processing includes polishing processes in which by means of relative movement of semiconductor wafer and polishing cloth under Force and supply of a polishing suspension (for example alkaline silica sol) a material removal is achieved. In the state The technique is batch double-side polishes ("double-side polishing ", DSP) and batch and single-wafer one-side polishes described (assembly of the semiconductor wafers by means of vacuum, bonding or adhesion during polishing processing one-sided on a pad).

The if necessary, final generation of layer structures takes place by epitaxial deposition, usually from the gas phase, oxidation, Vapor deposition (eg metallization) etc.

For the production of particularly flat semiconductor wafers, those processing steps are of particular importance, in which the semiconductor wafers are processed largely free of constraining forces "free-floating" without positive or positive clamping ("free-floating processing", FFP). FFP besei Particularly fast and with low material loss ripples, as they are generated for example by thermal drift or alternating load in the MWS. FFPs known in the art are lapping, DDG and DSP.

Especially advantageous is the use of one or more FFP at the beginning of Processing sequence, usually by means of a mechanical FFP, because by mechanical processing of the minimum material removal material especially for complete removal of the undulations done quickly and economically and the disadvantages of preferential etching the chemical or chemo-mechanical processing at high material abrasions is avoided.

The However, FFPs achieve the described advantageous features only if the procedures can be done this way that a largely uninterrupted processing of cargo to charge in the same rhythm is achieved. Interruptions for possibly necessary setting, dressing or sharpening processes or frequently necessary tool changes namely to unpredictable "cold start" influences, which negate the desirable features of the processes, and affect the economy.

The Lapping generates due to the brittle-erosive material removal by the rolling movement of the loosely supplied Läppkorns a very high damage depth and Surface roughness. This makes a complicated Post-processing to remove these damaged surface layers necessary, eliminating the benefits of lapping again be nullified. In addition, the lapping provides by depletion and sharpness loss of the supplied Korns during transport from the edge to the center of the semiconductor wafer always semiconductor wafers with unfavorably convex thickness profile with disc edges of decreasing thickness ("edge drop" the slice thickness).

The DDG basically causes a kinematic condition higher material removal in the center of the semiconductor wafer ("Looping") and, in particular with a small grinding wheel diameter, as he is structurally preferred in the DDG, also a marginal waste the slice thickness, as well as anisotropic - radially symmetric - processing marks, which strain the semiconductor wafer ("strain-induced warpage").

DE10344602A1 discloses a mechanical FFP process in which a plurality of wafers each lie in a recess of one of a plurality of carriers rotated by an annular outer and an annular inner drive ring and thereby held on a given geometric path and sandwiched between two rotating bonded abrasive media Working discs are machined material removing. The abrasive consists of a film or "cloth" adhered to the working disks of the apparatus used, such as in US Pat US6007407 disclosed.

However, it has been found that the wafers processed by this method have a number of defects, so that the resulting wafers are unsuitable for particularly demanding applications: For example, it has been found that semiconductor wafers with unfavorable spherical thickness profile generally result in pronounced edge drop , The semiconductor wafers often also have irregular ripples in their thickness profile and a rough surface with great depth of damage. The high depth of damage requires a complex post-processing, which has the advantage of in DE10344602A1 nullifies the disclosed method. The remaining crowning and the remaining edge drop lead to incorrect exposures during the photolithographic component structuring and thus to the failure of the components. Such semiconductor wafers are therefore unsuitable for demanding applications.

Furthermore, it has been found that, in particular when using the particularly preferred abrasive diamond, the rotor disc materials known in the prior art are subject to high wear and the generated abrasion impairs the cutting propensity (sharpness) of the working layer. This leads to an uneconomically short life of the carriers and makes frequent unproductive resharpening of the working layers necessary. It has also been found that carriers of metal alloys, in particular stainless steel, as used in the prior art during lapping and there have an advantageous low wear, are particularly unsuitable for carrying out the method according to the invention. For example, the known high solubility of carbon in iron / steel in (stainless) steel rotor discs leads to an immediate embrittlement and dulling of the diamond preferably used in the inventive method as an abrasive of the working layer. In addition, the formation of undesirable deposits of iron carbide and iron oxide layers on the semiconductor wafers was observed. It was found that high grinding pressures to force a self-sharpening of the dull working layer by pressure-induced forced wear, are unsuitable, since then the semiconductor wafers deformed who and the advantage of the FFP is nullified. In addition, the then increasingly occurring outbreak of whole abrasive grains leads to an undesirably high roughness and damage to the semiconductor wafers. The weight of the rotor disc leads to different degrees of dulling of upper and lower working layer and thus to different roughness and damage of the front and back of the semiconductor wafer. It turned out that the semiconductor wafer then becomes asymmetrically wavy, ie has undesirably high values for "bow" and "warp" (strain-induced warpage).

task

task The present invention is therefore to provide semiconductor wafers, which, due to their geometry, are also used to produce electronic Components with very small line widths ("design rules") suitable. In particular, it was the task of geometrical errors such as a thickness maximum in the center of the semiconductor wafer connected to a steadily decreasing thickness to the edge of the disc out, a marginal drop or a local minimum thickness in the center to avoid the semiconductor wafer.

Further also set the task, an excessive Surface roughness or damage of the semiconductor wafer to avoid. In particular, the object was a semiconductor wafer with low bow and warp to produce.

After all set itself the task to improve the grinding process so that a frequent replacement or restoration of Wear parts is avoided to an economical To enable operation.

solution

The Task is solved by a first method for simultaneous double-sided grinding of multiple wafers, each wafer freely movable in a recess of one of several by means of a Rolling device in rotation offset carriers and thereby moved on a cycloidal trajectory, wherein the semiconductor wafers between two rotating annular Working discs are machined material removing, with each Working disk includes a working layer, the bonded abrasive contains, characterized in that the shape of the between The work gaps formed during the working shifts during the Grinding is determined and the shape of the work surface at least one working disk mechanically or thermally dependent so changed by the measured geometry of the working gap is that the working gap has a predetermined shape.

The Task is also solved by a second method for simultaneous two-sided grinding of several semiconductor wafers, wherein each semiconductor wafer is freely movable in a recess one of several by means of a rolling device in rotation staggered carrier discs and thus on a cycloidal Trajectory is moved, the semiconductor wafers between two rotating annular working discs erosive material be processed, with each working disk a working shift comprising bonded abrasives thereby characterized in that the semiconductor wafers during the Processing temporarily with a part of their area leave from the working shifts limited working gap, where the maximum of the overflow in the radial direction more than 0% and at most 20% of the diameter of the semiconductor wafer is, with the overflow as the relative to the working wheels measured in the radial direction length is defined to the one semiconductor wafer to a certain When grinding over the inside or outside edge of the working gap.

The Problem is further solved by a third method for simultaneous two-sided grinding of several semiconductor wafers, wherein each semiconductor wafer is freely movable in a recess one of several by means of a rolling device in rotation staggered carrier discs and thus on a cycloidal Trajectory is moved, the semiconductor wafers between two rotating annular working discs erosive material be processed, with each working disk a working shift comprising bonded abrasives thereby characterized in that the rotor disc completely consists of a first material or a second material of the Rotor disc so with a first material completely or Partially coated is that during grinding only the first material in mechanical contact with the working layer and the first material does not affect the sharpness of the abrasive having reducing interaction with the working layer.

Each of the above methods is suitable for a semiconductor wafer with verbes verbes serten properties.

A Combination of two of the three or most preferably all three The above method is also suitable, a Semiconductor wafer with particularly improved properties manufacture.

Brief description of the figures

1 shows a device suitable for carrying out the method according to the invention in a perspective view.

2 shows a device suitable for carrying out the method according to the invention in a plan view of the lower working disk.

3 shows the principle of an inventively modified working gap between the working wheels of a device suitable for carrying out the method according to the invention.

4 shows radial profiles of the work disc formed by the two working wheels of a device suitable for carrying out the method according to the invention for different temperatures.

5 shows the cumulative frequency distribution of the TTV of semiconductor wafers, which were processed with inventively modified working gap, in comparison to the geometry distribution of semiconductor wafers, which were processed with non-inventively modified working gap. (TTV = total thickness variation, difference of the largest and smallest thickness of the semiconductor wafer)

6 shows the measured during processing gap of the working gap, which was held according to the invention by controlling the working disk shape approximately constant, and resulting surface temperatures at different locations in the working gap. (Gap = difference from the width of the working gap near the inner edge of the working disk and close to the outer edge of the working disk.)

7 shows the measured during processing gap of the working gap, which was not regulated according to the invention during processing, as well as the changing temperatures at different locations of the working gap.

8th shows the thickness profile of a semiconductor wafer, which has been processed by a method according to the invention, in which the semiconductor wafer temporarily leaves the working gap over part of the surface during processing.

9 shows the thickness profile of a semiconductor wafer, which has been processed by a non-inventive method in which the semiconductor wafer remains throughout the entire surface in the working gap.

10 shows the thickness profile of a semiconductor wafer, which has been processed by a method not according to the invention, in which the semiconductor wafer temporarily leaves the working gap over part of the surface during processing, but with an excessively large surface area.

11 shows the average rates of material removal of semiconductor wafers during successive processing runs with a method according to the invention, were used in the carrier according to the invention.

12 shows the average removal rates from successive processing runs with a method not according to the invention, in which non-inventive carriers were used.

13 shows the warp of a semiconductor wafer, which was processed by a method according to the invention, in comparison to a semiconductor wafer which has been processed by a method not according to the invention.

14 shows the surface damage depth ("sub-surface damage", SSD) of the front and back of a semiconductor wafer, which were processed by a method according to the invention with the same material removal by the two working layers of the device compared to a non erfindungsge machined disc with uneven material removal.

15 shows the surface roughness of the front and back of a semiconductor wafer, which was processed by a method according to the invention with the same removal of material through the two working layers of the device compared to a non-inventively processed disc with uneven material removal.

16 shows diametral sections of the thickness profile of a semiconductor wafer, which has been processed by a method according to the invention with controlled working gap.

17 shows diametral sections of the thickness profile of a semiconductor wafer, which was processed by a method not according to the invention processed with unregulated working gap.

18 shows the wear rate of the carriers in the "accelerated wear test" for different materials tested.

19 shows the ratio of material removal from the wafer and wear of the rotor in the "accelerated wear test" for different tested materials of the rotor discs.

20 Figure 12 shows the relative change in working layer chop length with "accelerated wear test" processing time for various materials of the rotor disks tested.

21 shows embodiments of inventive single-layer carriers (solid material).

22 shows embodiments of inventive multi-layer carrier wheels with full or partial coating.

23 shows embodiments of inventive carriers with partial coating in the form of one or more "knobs" or elongated "bar".

24 shows an embodiment of a carrier according to the invention, comprising a toothed outer ring and an insert.

25 shows the principle of the invention adjustment of the shape of a working disk by the action of symmetrical radial forces.

26 shows the principle of the regulation of the geometry of the working gap according to the invention by combining a rapid control of the temperature in the working gap and a slow control of the shape of the working disk.

1

upper working disk

4

lower working disk

7

internal drive rim

9

outer drive rim

11

upper work shift

12

lower work shift

13

rotor disc

14

recess for receiving the semiconductor wafer

15

Semiconductor wafer

16

Focus the semiconductor wafer

17

pitch circle Center of rotor disc in rolling device

18

reference point on semiconductor wafer

19

trajectory a point on the semiconductor wafer

21

Focus the rotor disk

22

Focus the rolling device

23

actuator for disc deformation

30

working gap

30a

width of the working gap outside

30b

width of the working space inside

34

drilling for the supply of resources

35

measuring device Working gap temperature (inside)

36

measuring device Working gap temperature (outside)

37

measuring device Working gap (inside)

38

measuring device Working gap (outside)

39

TTV distribution (machined with controlled working gap)

40

TTV distribution (with uncontrolled working gap)

41

Working gap difference while editing

42

temperature in the working gap outside

43

temperature in the working space inside

44

temperature in the middle of the work gap

45

thickness profile after processing with overflow

46

thickness profile after processing without overflow

47

bleed after processing without overflow

48

removal rate with sharpness unimpaired rotor disc

49

removal rate with sharpness reducing rotor disc

50

thickness profile in the direction of Notch

51

thickness profile 45 ° to Notch

52

average thickness profile

53

thickness profile 135 ° to Notch

54

Warp after asymmetric material removal

55

Warp after symmetrical material removal

56

notch with excessive overflow

57

temperature in upper working disk (volume)

58

Roughness / damages after symmetrical material removal

59

Roughness / damages after asymmetric material removal

65

thickness profile 90 ° to Notch

66

crown at uncontrolled working gap

67

Material reference numeral the rotor disk

68

wear rate the rotor discs

69

relationship from material removal of the semiconductor wafer and wear of the rotor disc

70

cutting capacity the work shift after 10 min

71

cutting capacity working shift after 30 min

72

cutting capacity working shift after 60 min

73

cutting capacity the work shift after 10 to 60 min

74

time Development of the cutting ability of the working shift (incomplete)

75

external teeth the rotor disk

76

recess in the rotor disk

77

lining the opening for receiving the semiconductor wafer

78

gearing for the positive connection of lining and rotor disc

79a

front Coating of the rotor disc

79b

rear Coating of the rotor disc

80

freed Edge in the coating of the rotor disc

81

partial-area Coating of the rotor disc in the form of a round "knob"

82

partial-area Coating of the rotor disk in the form of an elongated "bolt"

83

bonding the partial coating with the rotor disc

84

continuous, positive partial coating of the rotor disc

85

caulked (riveted) continuous partial coating of the rotor disc

86

toothed Outer ring of the rotor disc

87

commitment the rotor disk

90

measurand internal gap measuring sensor

91

Measured outside Gap measuring sensor

92

differential element distance signal

93

control element gap adjustment

94

manipulated variable gap adjustment

95

measurand internal temperature sensor

96

Measured outside temperature sensor

97

differential element temperature signal

98

control element Cleavage temperature adjustment

99

manipulated variable Cleavage temperature adjustment

A

relative Wear rate of the carrier

ASR

Working wheel radius

D

thickness

F

force

G

relationship From material removal of the semiconductor wafer and wear of the rotor disc ( "G-factor")

H

frequency (cumulative distribution)

MAR

middle removal rate

R

radius (the semiconductor wafer)

RG

relative Gap width (relative gap)

RMS

root-mean-square; roughness

S

relative Cutting ability of the working shift

SSD

sub-surface damage (near-surface damage)

t

Time (Time)

T

temperature

TTV

total thickness variation

W

warp (Ripple)

Description of a device that is for carrying out the inventive Method is suitable

1 shows the essential elements of a device according to the prior art, which is suitable for carrying out the method according to the invention. Shown is the schematic diagram of a two-disc machine for processing disc-shaped workpieces such as semiconductor wafers, as they are for example in DE10007390A1 is disclosed in perspective view ( 1 ) and in view of the lower working disk ( 2 ).

Such a device consists of an upper one 1 and a lower working disk 4 and one from an inner one 7 and an outer sprocket 9 formed rolling device, in the rotor discs 13 are inserted. The working wheels of such a device are annular. The carriers have recesses 14 holding the semiconductor wafers 15 take up. The recesses are usually arranged so that the midpoints 16 of the semiconductor wafers with an eccentricity e to the center 21 the rotor disc lie.

During machining, the working disks rotate 1 and 4 and the sprockets 7 and 9 with speeds n _o , n _u , n _i and n _a concentric about the center 22 the entire device (four-way drive). As a result, the carriers run on the one hand on a pitch circle 17 around the center 22 On the other hand, at the same time, they perform a self-rotation around their respective centers 21 , For any point of reference 18 a semiconductor wafer results with respect to the lower working disk 4 or working shift 12 a characteristic trajectory 19 (Kinematics), which is called trochoid. A trochoid is the generality of all regular, shortened or extended epi- or hypocycloids.

Upper 1 and lower working disk 4 wear working shifts 11 and 12 containing bonded abrasive. Suitable working layers, for example, describes US6007407 , The working layers are preferably designed so that they can be quickly assembled or disassembled. The one between the working shifts 11 and 12 formed gap is called a working gap 30 in which the semiconductor wafers move during processing. The working gap is characterized by a width which is dependent on the location (in particular on the radial position) and measured perpendicularly to the surfaces of the working layers.

At least one working disk, for example the upper one 1 , contains holes 34 through the work gap 30 Operating resources can be supplied, for example, a cooling lubricant.

To carry out the first method according to the invention, at least one of the two working disks, for example the upper one, is preferably provided with at least two measuring devices 37 and 38 of which preferably one ( 37 ) as close as possible to the inner edge of the annular working disk and a ( 38 ) are arranged as close to the outer edge of the working disk and make a non-contact measurement of the respective local distance of the working wheels.

Such devices are known in the art and for example in DE102004040429A1 disclosed.

For a particularly preferred embodiment of the first method according to the invention, at least one of the two working disks, for example the upper one, is additionally provided with at least two measuring devices 35 and 36 of which preferably one ( 35 ) as close as possible to the inner edge of the annular working disk and a ( 36 ) are arranged as close to the outer edge of the working disk and make a measurement of the temperature at the respective location within the working gap.

In the prior art, the working wheels of such devices usually include a device for setting a working temperature. For example, the working disks are provided with a cooling labyrinth, which is flowed through by a thermostat tempered coolant, such as water. For example, a suitable device is disclosed DE19937784A1 , It is known that the shape of a working disk changes as its temperature changes.

In the prior art devices are still known with which the shape of one or both working disks and thus the profile of the working gap between the working disks can be selectively changed by radial forces acting symmetrically on the working gap facing away from the working disk. So revealed DE19954355A1 a method in which these forces are generated via the thermal expansion of an actuating element which can be heated or cooled by a tempering device. Another possibility for targeted deformation of one or both working disks can be, for example, to generate the required radial forces F by means of a mechanically hydraulic adjusting device. By changing the pressure in such a hydraulic adjusting the shape of the working disk and thus the shape of the working gap can be changed. Instead of the hydraulic adjusting device, however, it is also possible to use piezoelectric (piezo crystals) or magnetostrictive (current-carrying coils) or electrodynamic adjusting elements ("voice coil actuators." In this case, the change in the shape of the working gap takes place in that the electric voltage or electric current is influenced in the control elements.

25a and 25b show schematically how the shape of the working nip 30 can be changed by an adjusting device 23 on the upper working disk 1 acts and this deformed.

With such devices can be adjusted specifically specifically convex or concave deformations of the working disk. These are particularly well suited to counteract the undesirable deformations of the working gap by the alternating loads during processing. Such concave (left) and convex (right) deformations of the working wheels are shown as a schematic diagram in 4 clarified. 30a denotes the width of the working gap 30 near the inner edge of the annular working disk and 30b the width of the working gap near the outer edge of the working disk.

Description of the first invention process

According to the first method of the invention, the shape of the working gap formed between the working layers is determined during grinding and the shape of the working surface of at least one working disk mechanically or thermally changed depending on the measured geometry of the working gap, that the working gap has a predetermined shape. Preferably, the shape of the working gap is controlled so that the ratio of the difference between the maximum and the minimum width of the working gap to the width of the working wheels at least during the last 10% of the material removal is at most 50 ppm. The term "width of the working disks" is understood to mean their ring width in the radial direction. If the entire surface of the working disks is not covered by a working layer, the term "width of the working disks" should be understood to mean the annular width of the working disk surface of the working disks , "At least during the last 10% of the material removal" means that the condition "at the most 50 ppm" during the last 10 to 100% of the material removal is fulfilled. This condition can therefore also be fulfilled according to the invention during the entire grinding process. "At most 50 ppm" means a value in the range of 0 ppm to 50 ppm. 1 ppm is equivalent to the number 10 ^-6 .

Preferably During grinding, the gap progression continues by means of at least two in at least one of the working wheels built-in non-contact distance measuring sensors measured and by means of targeted deformation at least one of the two working disks constantly readjusted, that despite registered during processing thermal Wechsellast, which is known to be an undesirable Deformation of the working wheels always produces a desired one Work gap course is obtained.

In a preferred embodiment of the first method according to the invention, the above described cooling labyrinths used in the working wheels for regulating the working disk shape. It is first determined the radial profile of the working gap in the idle state of the grinding device used for several temperatures of the working wheels. For this purpose, for example, the upper working disk is brought with three identical final dimensions at fixed points and under a fixed load on nominally uniform distance to the lower working disk and determines the radial profile of the resulting gap between the working wheels, for example, with a micrometer. This is done for different temperatures of the cooling circuit of the working wheels. In this way one obtains a characterization of the change in shape of the working disks and the working gap as a function of the temperature.

While The processing is then performed by continuous measurement with the contactless distance measuring sensors a possible change the radial working gap profile determined by targeted change the working disk temperature control in accordance with the known Temperature characteristic so counteracted that the working gap always maintains the desired radial profile. This happens, for example, by the flow temperature of the thermostats for the cooling labyrinths of working disks during the editing is changed specifically.

this first method of the invention is the observation underlying that is always an undesirable while editing Form change of the working gap occurs, which coincides with Measures according to the prior art such as a constant Arbeitsscheibentemperierung can not be avoided. Such an undesirable gap change is for example by the entry of thermal exchange rates during processing. This may be the while the material removal during machining performed on the workpiece Depending on the processing progress with the varying sharpness state of the grinding tool fluctuates. Also occur mechanical deformations the work disks as a result of the usually during the Machining selected different machining pressures (Load of the upper working disk) and also by varying Tumble the work disk at different processing speeds (Kinematics). Another example of varying Machining conditions leading to undesirable deformation of the working disks are chemical reaction energies with the addition of certain equipment in the working gap. After all lead the power losses of the device drives themselves to continuously changing operating conditions.

In another embodiment of this first method is the temperature of the working gap with the working gap during operating medium supplied to processing (cooling lubricant, "grinding water") made by its temperature flow or its volume flow is varied so that the working gap the desired Takes shape. Particularly advantageous is the combination of both control measures, since the reaction times of the change in shape by the temperature the working disk and the grinding water supply different and thus a regulation which is even better adapted to the requirements of the working gap is possible. The rule requirements vary for example, with varying desired material removal, different grinding pressures, different cutting properties different working shifts etc.

Prefers is also the use of temperature sensors that control the temperature in the working gap at different places during processing determine (temperature profile). It has been shown that undesirable changes in the shape of the working gap during processing often changes in temperature precede in the work gap. By inventive Control of the shape of the working gap based on these temperature changes can be a particularly fast control of the shape of the Reach working gaps.

The regulation of the shape of the working gap can thus by measures of direct deformation of at least one of the working wheels, for example by the described hydraulic or thermal deformation device, or the indirect change in shape by changing the temperature or amount of the working gap supplied operating means (whereby a change in temperature of the working gap and thus also the working disks is effected, which change the shape of the working gap) are made. Particularly advantageous is a regulation of the working gap on a detection of the widths of the working gap or the temperatures prevailing therein, feedback of the measured values in the control unit of the device and tracking of pressure or temperature (direct change in shape) or temperature and quantity (indirect change in shape) a closed loop. For both methods - the direct or indirect change in the shape of the working gap - the width or the temperature of the working gap can be used to determine the deviation. The use of the measured width of the working gap to determine the control deviation has the advantage of taking into account the gap deviation (in micrometers) and the disadvantage of the time delay. The use of the gem in the working gap These temperatures have the advantage of higher speed, as deviations are already taken into account, even before the working disk has deformed, and the disadvantage that an exact foreknowledge of the dependence of the shape of the working gap on the temperature must be present (reference gap profiles).

A particularly advantageous embodiment consists in one Combination of both methods. Preferably, the shape of the working gap because of the high speed of this scheme on a short time scale regulated on the basis of the measured temperatures in the working gap. The measured widths of the working gap on the inner and outer Edge of the working wheels, however, are preferably used to on a long time scale drift of the form of the Determine working gap and possibly counteract this drift.

An embodiment of this particularly advantageous embodiment is shown schematically in FIG 26 shown. In a first, slow loop the non-contact distance sensors send 37 and 38 continuously measuring signals 90 and 91 via a difference element 92 to a control element 93 , This control element sends a manipulated variable 94 to an actuator for disc deformation 23 , Thus, a slow drift of the geometry of the working gap can be corrected. In a second, fast control loop, the temperature sensors send 35 and 36 measuring signals 95 and 96 to a control element 98 , whose manipulated variable 99 depending on the predetermined target temperature profile on the temperature and / or on the flow rate of a supplied into the working gap cooling lubricant acts. This can be counteracted a change in temperature in the working gap, even before it comes to influencing the gap geometry.

It has been shown that the greatest evenness of Semiconductor wafers when processed by the invention Method is achieved when the working gap during the Machining in the radial direction a largely uniform Has width, d. H. the work disks are parallel to each other or have a slight gap from the inside to the outside. Therefore, in a further embodiment, this is preferred first method a constant or slightly from the inside to outside widening working gap. In the case of an exemplary Device whose working wheels have an outer diameter of 1470 mm and an inner diameter of 561 mm the width of the working wheels consequently 454.5 mm. The distance sensors are due to their finite mounting size not exactly at the inner and outer edge of the working disk, but on pitch diameters of 1380 mm (outer Sensor) or 645 mm (inner sensor), so that the sensor distance 367.5 mm, that is about 400 mm. As particularly preferred a radial course of the width of the working gap between inner and outer sensor in the range of 0 microns (Parallel course) up to 20 μm (expansion from inside to outside). The ratio of the difference between the width of the working gap on the outside and inner edge to the width of the working wheels, which in the measurement is taken into account, so is particularly preferred between 0 and 20 μm / 400 mm = 50 ppm.

The suitability of this first method for solving the problem underlying the invention of providing particularly flat semiconductor wafers is illustrated by the figures 5 . 6 . 8th and 17 ,

5 shows the frequency distribution H (in percent) of the TTV of semiconductor wafers which have been processed with working gap controlled according to the invention by means of cooling labyrinths and measuring the width of the working gap ( 39 ), compared to the distribution of the TTV of semiconductor wafers which have been processed with a working gap which is not regulated according to the invention ( 40 ). The work gap control method according to the invention leads to significantly better TTV values. (The TTV = "total thickness variation" denotes the difference between the largest and smallest thickness measured across the entire wafer.) The TTV values shown were determined by a capacitive measurement method.)

If for the processing of the semiconductor wafers by the invention Process requires a particularly low total material removal is, the processing time is often shorter than the reaction time of the described invention Measures for working gap regulation. It has shown, that it is sufficient in such cases when the working gap at least towards the end of processing, d. H. during the last 10% of material removal, with the preferred radially homogeneous Wide or slight gaping from the inside out.

6 shows the difference measured in a method according to the invention 41 from the width of the working gap near the inner diameter and close to the outer diameter of the working wheels during machining. The total processing time was about 10 minutes. A total material removal of the semiconductor wafers of 90 μm was achieved. The average removal rate was thus about 9 μm / min. The working gap ver runs, except for the pressure build-up phase within the first 100 s, according to the invention in parallel or with a slight gap. The gap widening from the inside to the outside at the end of the processing is according to the invention about 15 microns.

Shown are also measured during processing temperatures at different locations of the one hand, the working gap limiting surface of the upper working disk near the inner diameter of the annular working disk ( 43 ), in the middle ( 44 ) and close to the outer diameter ( 42 ), as well as the mean temperature 57 in the volume of the work disk. Shape and temperature of the working disk were controlled by the described inventive method so that the working gap according to the invention runs over the entire processing time in parallel or with a slight gap. (G = "gap difference", difference between internal and external measured gap width, ASV = temperature at the working disk surface in the volume, ASOA = temperature at the working disk surface outside, ASOI = temperature at the working disk surface inside, ASOM = temperature of the surface in the middle between "Inside" and "outside", T = temperature in degrees Celsius, t = time).

16 shows the associated thickness profile of this invention processed with controlled working gap semiconductor wafer. Shown are four diametrical profiles of thickness, performed below 0 ° ( 50 ), 45 ° ( 51 ), 90 ° ( 65 ) and 135 ° ( 53 ) to the notch of the semiconductor wafer. 52 gives the averaged over the four individual profiles diametral profile again. (D = local thickness in microns, R = radial position of the wafer in millimeters). The measured values were determined by a capacitive thickness measurement method. The TTV, ie the difference between the largest and smallest thickness over the entire semiconductor wafer, is in the example shown, the processed according to the invention with a controlled working gap semiconductor wafer 0.55 microns.

7 shows as a comparative example the course of working gap difference 41 and temperatures inside 43 , in the middle 44 , Outside 42 and in volume 57 in a method not according to the invention. Temperatures and shape change as a result of the described thermal and mechanical alternating loads introduced during machining. The working gap was not readjusted and has at the end of processing a non-inventive narrowing by about 25 microns from the inside out.

17 shows the associated thickness profile of the semiconductor wafer not processed according to the invention in the comparative example, in which the working gap was not controlled according to the invention during processing. Clearly visible is the extreme crowning of the obtained semiconductor wafer, with a pronounced point of maximum thickness 66 , Due to the size of the device used (ring width of the working disk 454.5 mm) and the size of the semiconductor wafers (300 mm), each rotor disk can accommodate only one semiconductor wafer. The eccentricity e of the center 16 the semiconductor wafer with respect to the center 21 the rotor disk was e = 75 mm ( 2 ). Accordingly, the point lies 66 maximum thickness about 75 mm eccentric with respect to the center of the semiconductor wafer ( 16 ). In particular, the resulting semiconductor wafer is not rotationally symmetrical. The TTV of the semiconductor wafer shown in the comparative example not according to the invention is 16.7 μm.

Description of the second invention process

in the The following is the second method according to the invention described in more detail: In this method leave the semiconductor wafers during processing temporarily with a certain Proportion of their area the working gap and the kinematics The processing is preferably chosen so that due this "overflow" of the semiconductor wafers in the barrel the processing gradually including the entire surface of the working shifts their marginal areas completely and substantially the same is often repainted. The "overflow" is as measured relative to the working wheels in the radial direction Defined to be a semiconductor wafer to a length certain time during grinding over the inner or outer edge of the working gap is also. According to the invention, the maximum of the overflow in the radial direction more than 0% and at most 20% of Diameter of the semiconductor wafer. For a semiconductor wafer with a diameter of 300 mm, the maximum overflow therefore more than 0 mm and not more than 60 mm.

This second method according to the invention is based on the observation that, in the comparative example of a grinding process in which the semiconductor wafers always remain completely within the working gap, a trough-shaped radial profile of the working layer thickness results in the course of wear of the working layers. This has measurements of the gap profile according to the method 4 shown.

The greater thickness of the working layer to the inner and outer edges of the annular work discs out leads to a reduced there work gap, a higher material removal of those areas of the half causes this area in the course of processing. The semiconductor wafer receives an undesirable crowned thickness profile with decreasing thickness toward its edge ("edge drop").

Become now in the context of the second method according to the invention the conditions chosen so that the semiconductor wafer temporarily over the inner and outer edges the working layers out, takes place over the entire ring width of the working layer radially substantially uniform Wear, it forms no trough-shaped radial profile the working layer thickness, and there is no edge drop the so Semiconductor wafer machined according to the invention causes.

In an embodiment of this second method is the Eccentricity e of the semiconductor wafer in the rotor disc chosen so large that while editing an inventive temporary partial overflow of the semiconductor wafer over the edge of the working layer takes place.

In another embodiment of this second method The working layer is annular at the inner and outer edges trimmed so that during processing an inventive temporary partial overflow of the semiconductor wafer over beyond the edge of the working shift.

In another embodiment of this second method becomes a device with such a small diameter of the working wheels selected; that the semiconductor wafer according to the invention temporarily Partial over the edge of the working wheels amounts.

Especially preferred is also a suitable combination of all three mentioned Embodiments.

The Requirement of this second method according to the invention, that the semiconductor wafers gradually cover the entire area the working shifts including their edge areas sweep completely and essentially the same number of times, is fulfilled by the fact that the main drives of a Inventive implementation of the method suitable device usually AC servomotors (AC = alternating current, English current "), where basically a variable Delay between setpoint and actual speed occurs (drag angle). Even if the speeds for the drives so chosen will result in nominally periodic orbits that are particularly unfavorable for the implementation of the invention Are due to the AC servo control in the Practice always ergodic (aperiodic) paths. This is the above Demand always met.

8th shows the thickness profile 45 a processed according to the second method of the invention semiconductor wafer with a diameter of 300 mm. The overflow was 25 mm. The semiconductor wafer has only small random variations in thickness and in particular has no edge drop. The TTV is 0.61 μm.

9 gives as a comparative example the thickness profile 46 a not processed according to the invention semiconductor wafer with a diameter of 300 mm again, during its processing, the semiconductor wafer was always the entire surface in the working gap. This results in a pronounced reduction in thickness 47 in the edge region of the semiconductor wafer. The TTV is over 4.3 μm.

10 As a further comparative example, the thickness profile of a semiconductor wafer not processed according to the invention having a diameter of 300 mm, in the processing of which the overflow was not large according to the invention, namely 75 mm, is given. There are clearly pronounced notches 56 at a distance from the edge of the wafer corresponding to the width of the overflow (75 mm).

It has been shown that in case of excessive overflow due to the lack of leadership of the semiconductor wafer outside the working gap, the semiconductor wafer due to deflection of semiconductor wafer or rotor partially emerges in the axial direction from the leading recess of the rotor. Upon reentry of the overflowing part of the semiconductor wafer into the working gap, the semiconductor wafer is then supported by a part of its generally rounded edge on the edge of the carrier disc recess. If the overflow is not too great, the semiconductor wafer is forced back into the recess upon re-entry into the working gap; if the overflow is too high, this will not succeed and the semiconductor wafer will break. This "snapping back" into the carrier disc recess leads to excessive material removal in the region of the edge of the working layer 10 occurring notches 56 , The TTV of the semiconductor wafer of the comparative example is 2.3 μm. The notches 56 are particularly harmful because roughness and depth of damage are increased due to the there stronger material removal and the strong curvature of the thickness profile in the Einkerbun gene 56 particularly unfavorable effect on the nanotopology of the semiconductor wafer.

According to the invention the overflow is more than 0% and less than 20% of the diameter the semiconductor wafer and preferably between 2% and 15% of the diameter the semiconductor wafer.

Description of the third invention process

in the The following is the third method according to the invention described in more detail. In this process, runners with a well-defined interaction with the working layers used. According to the invention, the carriers go either a very small interaction with the working layers so that the latter does not interfere with their cutting behavior or the runners go a particularly strong, the working layer targeted roughening interaction with the working layers one, so that the latter continuously during processing be sharpened. This is achieved by a suitable Choice of material of the carriers.

the third method of the invention is the following Observation based on the materials known in the art for carriers are for carrying the grinding process completely unsuitable. armature discs made of metal, as for example when lapping and when Double-side polishing used are subject to the grinding process an extremely high wear and go one undesirable strong interaction with the working shift one. In the working layers is preferably diamond as Abrasivum contain. The observed high wear is in the known high abrasive action of diamond based on hard materials; the undesired interaction exists, for example in that the carbon made of the diamond, in particular alloyed in iron metals (steel, stainless steel) at a high rate. The diamond embrittles and quickly loses its cutting action, so that the working shift becomes dull and sharpened must become. Such frequent sharpening leads to uneconomic consumption of working shift material, unwanted frequent interruptions of processing and too unstable Machining processes with poor results for Surface texture, shape and thickness constancy of so processed semiconductor wafers. There is also a contamination the wafer with metallic abrasion undesirable. Similar Unfavorable properties were also found on other carrier disc materials which have also been tested, for example aluminum, Anodized aluminum, metallic coated carriers (For example, hard chromed protective layers or layers Nickel-phosphorus).

To the state of the art are wear protection coatings the carrier disc made of materials of high hardness, low coefficient of sliding friction and according to comparison tables low abrasion known under friction. While these for example, when polishing double side very low wear are and thus coated carriers up to a few Withstand a thousand processing cycles, it turned out that such Non-metallic hard coatings in the grinding process an extremely subject to high wear and are therefore unsuitable. Examples are ceramic or glassy (enamel) coatings as well as diamond-like carbon coatings (DLC, diamond-like carbon).

It It was further observed that in the grinding process, every one examined Material for the rotor disc one more or less subject to high wear and that occurring Material abrasion usually interacts with the working layer received. This usually leads to a quick loss of sharpness (Cutting ability) or a heavy wear of the working shift. Both are undesirable.

Around find suitable materials for carriers, which do not have the disadvantages mentioned, has become a variety examined by pattern runners. It turned out that some materials or coatings of the carrier, if they are only subject to the action of the working class alone, actually have the expected properties. For example turn out to be commercially available so-called "lubricious coatings" or "wear protective coatings", for example made of polytetrafluoroethylene (PTFE) as resistant to the effect of the working shift alone. When coated like this Runners but when carrying out the invention Method of action of the working layer and the action of the generated by the processing, for example, silicon-containing Abrasive sludge, it was found, wear out These sliding or protective coatings extremely fast.

This lies in the fact that the firm in the working shift bonded diamond one grinding and the loose in the silicon slurry produced contained silicon, silica and other particles Create lapping effect. This mixed load of loops and lapping poses a completely different burden on the carrier materials are as they are by grinding or lapping each alone.

For the realization of the third method according to the invention, a multiplicity of carriers made of different materials were produced and subjected to a comparison test for determining material wear and interaction with the working layer. This "accelerated wear test" is described below: It is a device suitable for carrying out the method according to the invention according to 1 and 2 used. The upper working disc is not used during the test and is swung out. Before the start of the test series of a rotor disc material, the lower working layer 12 each fresh and sharpened with a constant sharpening process to create the same starting conditions. The average thickness of a rotor disk 13 From a material whose wear and interaction behavior is to be investigated is measured in several points (microns) and, alternatively, with knowledge of the specific weight of rotor and coating, determined by weighing. The rotor disk is in the rolling device 7 and 9 inserted and uniformly loaded with a first weight. The average thickness of a semiconductor wafer 15 is measured or, preferably, determined by weighing. The semiconductor wafer is placed in the rotor and uniformly loaded with a second weight. The lower working disk 4 with the lower working shift 12 and the rolling device 7 and 9 are set in motion at fixed preselected speeds for a certain period of time. After the time has elapsed, the movement is stopped, the rotor disk and the semiconductor wafer are removed and, after cleaning and drying, their average thicknesses are determined. During the movement of the working disk and the rolling device relative to the rotor disk and the semiconductor wafer under load, material wear (undesired wear) from the rotor disk and removal of material from the semiconductor wafer (desired grinding action) takes place. This sequence of weighing, wear / erosion and weighing is repeated several times.

18 shows the thus determined average thickness loss (wear rate A) of carriers in μm / min for a variety of materials in logarithmic application. The materials coming into contact with the working layer and the grinding sludge from the removal of the semiconductor wafer during the test 67 the runners and the experimental conditions are given in Table 1. Table 1 also indicates whether the material of the carrier disc which came into contact with working layer and grinding sludge was present as a coating ("layer", for example applied by spraying, dipping, brushing and optionally subsequent hardening), as a film or as a solid material Abbreviations used in Table 1 mean: "GRP" = glass fiber reinforced plastic, "PPFK" = PP fiber reinforced plastic The abbreviations for the various plastics are the commonly used: EP = epoxy, PVC = polyvinyl chloride, PET = polyethylene terephthalate (polyester), PTFE = polytetrafluoroethylene, PA = polyamide, PE = polyethylene, PU = polyurethane and PP = polypropylene ZSV216 is the manufacturer's name of a tested lubricious coating and kraft paper is a paper fiber reinforced phenolic resin "ceramic" refers to microscopic ceramic particles embedded in the given EP matrix. "Cold" refers to the application by means of a self-adhesive foil back and "hot" a hot lamination process in which the equipped with hot melt adhesive film back was connected by heating and pressing with the rotor core. The column "LS load" indicates the weight load of the carrier during the wear test.The weight load of the wafer was in all cases 9 kg. contraction Rotor discs material kind application LS load layer foil Full Mater. [Kg] a EP-GRP X 2 b EP-GRP X 4 c PVC film X 2 d PVC film X 4 e PET (cold) X 2 f PET (hot) X 4 G EP-CFK X 4 H PP-GFK X 4 i PP PPFK X 4 j Laminated paper X 4 k PTFE II X 4 l PA film X 4 m PE (I) X 4 n PE (II) X 4 O PU X 4 p EP / Ceramic X 4 q EP (primer) X 4 r Gleitbesch. ZSV216 X 4 Table 1: Carrier pulley materials for wear test

It can be seen that the different materials for the carrier disc under the complex mixing load of abrasive action through the working layer and lapping action by the grinding slurry due to the removal of material from the wafer result in very different wear rates for the carrier. The value for material i (PP fiber reinforced PP) could not be reliably determined (dashed line for measuring point and error bar in) 18 ). For example, the lowest wear rates are PVC (c for 2 kg test load and d for 4 kg test load), PET (e for a thermoplastic self-adhesive film at 2 kg test load and f for a crystalline PET film applied by a heat-laminating process), PP (h) and PE (m for a very thin, soft film of LD-PE and n for a thicker, harder film of different molecular weight LD-PE). A particularly low wear rate is achieved with an elastomeric PU (o).

19 shows the ratio of material removal achieved during a test run from the semiconductor wafer and the measured wear of the rotor disk. In this application, the cutting ability (sharpness) of the working layer freshly dressed before the start of the test is immediately taken into account. Some rotor disk materials quickly blunt the working layer so that only a lower removal rate for the wafer is achieved and the ratio of carrier wear and wafer removal becomes even less favorable. Advantageously high values for the so-called "G-factor" (span ratio) provide carriers of PVC (c and d), PET (e and f) and ceramic particles filled EP (p), but the ratio determined for PU (o) is still more than a factor of ten higher than that of the aforementioned materials.

20 shows the interaction of the abrasion of the rotor disc material with the working layer. Shown are the respective removal rates 73 under the constant test conditions after every 10 min test duration ( 70 ), 30 min ( 71 ) and 60 minutes ( 72 ), based on the average removal rates of the reference material c (PVC film at 2 kg test load). A decrease in the removal rate of the working layer over time is undesirable. Such a rotor disc quickly blunts the working layer and would result in frequent re-sharpening and unstable and uneconomical work processes. For some rotor disk materials, the sharpness of the working layer decreases so rapidly that it is completely blunt at 30 minutes or 60 minutes, or the rotor disk of the material was so unstable that after a few minutes it was completely worn or broken (dashed lines 74 For example, for Pertinax (a phenol resin impregnated paper, commonly referred to as "hard paper") j, PE film m or the tested EP primer coating q or The "wear-resistant coating" ZSV216 r. As advantageous with respect to low dullness of the sharpness of the working layer, carriers are made of the materials PA ( 1 ) and PE (n). However, an elastomeric PU (o) is particularly stable and has a low blunting effect on the sharpness of the working layer.

Further, it shows in 20 in that rotor disc materials in which a fiber-reinforced layer comes into contact with the working layer leads to a particularly rapid dulling of the working layer. The grinding action of the working layer is, for example, for EP-GRP (a and b), EP-CFK (g) and PP -GFK (h) dropped drastically after 10 minutes and comes to a standstill after a few more minutes. In comparison to the glass fiber reinforced EP (a and b), a coating of EP without glass fibers (p) blunts the working layer much more slowly. Therefore, it is preferable that the first material contains no glass fibers, no carbon fibers and no ceramic fibers.

For a first embodiment of this invention third method (low-interaction rotor disk) a rotor disc is used which is completely made of a first material or a full or partial coating from a first material so wears during working only this layer in contact with the working layer passes, this first material high abrasion resistance having.

Prefers for this first material are polyurethane (PU), polyethylene terephthalate (PET), Silicone, Rubber, Polyvinyl chloride (PVC), Polyethylene (PE), Polypropylene (PP), polyamide (PA) and polyvinyl butyral (PVB), epoxy resin and phenolic resins. Furthermore, polycarbonate (PC), Polymethylmethacrylate (PMMA), polyetheretherketone (PEEK), polyoxymethylene / polyacetal (POM), polysulfone (PSU), polyphenylene sulfone (PPS) and polyethylenesulfone (PES) can be used to advantage.

Especially Preference is given to polyurethanes in the form of thermoplastic elastomers (TPE-U). Also particularly preferred are silicones as silicone rubber (Silicone elastomer), silicone rubber or silicone resin, also rubber in the form of vulcanized rubber, butadiene styrene rubber (SBR), acrylonitrile rubber (NBR), ethylene-propylene-diene rubber (EPDM), etc. and fluororubber. Further, PET is particularly preferred as partially crystalline or amorphous Polymer, in particular thermoplastic co-polyester-based elastomer (TPE-E), and polyamide, in particular PA66 and thermoplastic polyamide elastomer (TPE-A), and polyolefins such as PE or PP, in particular thermoplastic Olefin elastomers (TPE-O). Finally, it is particularly preferred PVC, in particular plasticized (soft) PVC (PVC-P).

Also fiber-reinforced are preferred for coating or solid material Plastics (compound plastics, fibrereinforced plastics, FRP), wherein the fiber reinforcement is not made of glass fibers, carbon fibers or ceramic fibers. Especially preferred for the fiber reinforcement is natural fibers and synthetic fibers, for example cotton, cellulose etc. and polyolefins (PE, PP), Aramids etc.

Exemplary embodiments of carriers according to the invention are shown in the figures 21 to 24 again. 21 shows runners 15 , which consist entirely of a first material (single-layer carriers). Exemplary is in 21 (A) a rotor disc with an opening 14 shown for receiving a semiconductor wafer and in 21 (B) one with several openings 14 for simultaneous recording of several semiconductor wafers. The carriers comprise adjacent to these receiving openings always an external toothing 75 which engages in the rolling device formed by the inner and outer pin ring of the processing machine, and optionally one or more openings or openings 76 , which primarily serve the better flow and replacement of the working fluid supplied cooling lubricant between the front and back (upper and lower working layer).

21 (C) shows in a further embodiment, a single-layer rotor according to the invention of a first material, wherein the opening 14 for receiving the semiconductor wafer with a third material 77 is lined. This extra lining 77 is preferred when the first material of the rotor disc 15 is very hard and in direct contact with the semiconductor wafer would lead to an increased risk of damage in the edge region of the semiconductor wafer. The third material of the lining 77 is then chosen softer, so that edge damage is excluded. The lining is, for example, by gluing or positive locking, optionally by means of a contact surface enlarging "dovetail" 78 as in the embodiment in 21 (C) shown with the rotor disc 15 connected. Examples of suitable third materials 77 are revealed in EP 0208315 B1 ,

It is also preferable if the carrier disc has a core which does not come into contact with the working layer and made of a material having a higher rigidity (modulus of elasticity) than that in contact with the working part layer having coating. Especially preferred for the rotor core are metals, in particular alloyed steels, in particular corrosion-protected (stainless steel) and / or spring steels, and fiber-reinforced plastics. The coating, ie the first material, in this case preferably consists of an unreinforced plastic. The coating is preferably applied to the core by means of deposition, dipping, spraying, flooding, hot or hot bonding, chemical bonding, sintering or positive locking. The coating can also consist of individual dots or strips, which are inserted by joining or pressing, injection molding or gluing in appropriate holes in the core.

Embodiments of such multi-layer carriers comprising a core 15 from the second material and a front ( 79a ) and back coating 79b from the first material, shows 22 , 22 (A) describes a rotor disk, in which the front and back over the full surface of the core 15 is coated while 22 (B) a partially coated rotor disc describes, in the embodiment shown, for example, an annular region 80 was released at the opening for receiving the semiconductor wafer and at the outer toothing of the rotor disc.

Advantages of partially coated carrier discs according to example in 22 (B) include that z. B. the edge of the opening for receiving the semiconductor wafer with a lining of a third material 77 as in 21 (C) can be provided only with the harder second material of the core 15 is connected and can be attached either before or after the coating, or that z. B. the area of the external teeth is kept free of the low-wear first material and thereby disturbing material abrasion during rolling in the rolling device of the processing machine is avoided.

For the plastics of a not coming into contact with the working layer Kerns is a fiber reinforcement of stiff fibers, for example Glass or carbon fibers, esp. Ultrahochmodul carbon fibers, preferably.

Especially the coating is preferably in the form of a prefabricated film by means of lamination in a continuous process (roll lamination) applied. The film is back with a cold glue or, more preferably, with a hot or hot glue coated (hot lamination), consisting of base polymers TPE-U, PA, TPE-A, PE, TPE-E or ethylene vinyl acetate (EVAc) or the like.

Further is preferred if the rotor disc from a stiff Core and individual spacers exists, with the spacers consist of an abrasion-resistant material with low sliding resistance and are arranged so that the core during processing not in contact with the working layer.

Embodiments for carriers with such spacers are 23 again. The spacers may, for example, be front- 81a ) and back ( 81b ) applied "pimples" or "dots" 81 or oblong "bars" 82 each arbitrary shape and in any number ( 23 (A) ). These spacers 82a (Front of the rotor) and 82b (Back), for example, by gluing, z. B. by means of a back-side self-adhesive coating 83 the individual coating elements 82 (and 81 ), with the rotor disc 15 be connected ( 23 (B) ) or positively fit into holes in the rotor disc ( 84 ) or by caulking, riveting, fusing, etc., for example mushroom-shaped at the front and back of the rotor widened (pressed, etc.) through holes in the rotor disc passing elements 85 be. Also, a front ( 79a ) and back ( 79b ) Coating according to the embodiments in 22 by means of several extending through holes in the rotor disc webs according to the example of the coating elements 84 respectively. 85 in 23 (B) be connected to each other and thereby an additional safeguard against unwanted detachment of the applied coating 79 deliver.

After all it is preferred that the core of the second material exclusively from a thin outer annular Frame of the rotor disc is made, this ring the Gearing of the rotor disc for the drive through includes the rolling device. One from the first material existing insole comprises one or more recesses for one semiconductor wafer each. Preferably, the first material by positive locking, gluing or injection molding with the annular Frame connected. Preferably, the frame is much stiffer and lower wear than the insert. While the processing is preferably only the deposit in contact with the working shift. Particularly preferred is a steel frame with an insert of PU, PA, PET, PE, PE-UHWM, PBT, POM, PEEK or PPS.

As in 24 it is preferred that the annular frame 86 with the toothing thin ner is considered the deposit 87 and substantially centered to the thickness of the insert 87 connected to this, so that the frame of the second material does not come into contact with the working layers of the processing device. The connection between insert 87 and frame 86 is preferably made blunt, as in the form-fitting pressed spacer 84 in 23 (B) shown, or consists in a broadening of the deposit 87 after the example of the spacer 85 in 23 (B) over the edge of the frame 86 out.

Especially preferred is, if the aforementioned, by contact with the working layer Wear-related spacers by joining in holes in the core or by sticking to the surface of the core can be easily replaced.

Also it is particularly preferred that the worn partial or full surface Coating easily detached from the core and by applying a new coating can be renewed. The detachment The easiest way to do this for suitable substances is to use suitable solvents (for example, PVC by tetrahydrofuran, THF), acids (For example, PET or PA by formic acid) or by Heating in an oxygen-rich atmosphere (incineration).

in the Case of a core of an expensive material, such as stainless steel or consuming by material removal (grinding, lapping, Polishing) to thickness calibrated, tempered or otherwise aftertreated or coated metal such as steel, aluminum, titanium or alloys this, high performance plastic (PEEK, PPS, POM, PSU, PES o. if necessary with an additional fiber reinforcement) etc. is a reuse of the rotor after extensive wear of the coating by repeated newly applying the wear coating preferred. Especially The coating is preferably in the form of a film, which by means of Punching, cutting plotter o. Ä. Previously fit exactly to the dimensions the carrier was cut, by means of lamination applied congruently, so that no rework such as trimming possibly superior Parts of the coating, edges overcast, deburring, etc. is required. In the case of a core made of high-performance plastic particularly preferred is a remainder of the worn first coating remain.

in the Case of a core of a cheap material, for example a possibly additionally fiber reinforced plastic such as EP, PU, PA, PET, PE, PBT, PVB or the like, becomes unique Coating preferred. The coating is done especially prefers already on the blank (panel) for the core, and the rotor disc is only from the back Coating, core and front coating formed "sandwich" panel by means of milling, cutting, water jet cutting, laser cutting o. Ä. Separated. After wear of the coating almost to the core is the rotor disc in this Embodiment then discarded.

11 gives, as an example, the average removal rate MAR of the semiconductor wafer obtained for successive processing journeys F, whereby a carrier disc not influencing the sharpness of the working layer was used. The average removal rate remains essentially constant over the 15 processing cycles shown here ( 48 ). The material removal from the semiconductor wafer during a processing cycle was 90 μm. The rotor disc consisted of a stainless steel core, which was provided on the front and back with a 100 micron thick PVC coating. The thickness decrease of this coating due to wear was on average 3 microns per processing cycle.

12 gives, as a comparative example, the mean removal rate MAR of the semiconductor wafer obtained for successive processing runs F, using a non-inventive carrier disc which had a work layer reducing action. The average rate of material removal decreases continuously from one cycle to the next, starting from more than 30 μm / min down to less than 5 μm / min within the 14 machining cycles shown. The rotor disk consisted of glass fiber reinforced epoxy resin. The thickness decrease of this coating due to wear was on average 3 microns per processing cycle.

For a second embodiment of the third invention Procedure ("sharpening rotor") a rotor disc is used which is completely consists of a second material or a coating of the parts, which come in contact with the working layer, from a second Carries material, this second material containing substances, which sharpen the working shift.

It is preferred that this second material contains hard materials and is subject to wear on contact with the working layer, so that by the wear hard substances are released, which are the working layer sharpen. It is particularly preferred that the hard materials released during the wear of the second material are softer than the abrasive contained in the working layer. Particularly preferred is when the released material is corundum (Al ₂ O ₃ ), silicon carbide (SiC), zirconium oxide (ZrO ₂ ), silicon dioxide (SiO ₂ ) or ceria (CeO ₂ ) and the abrasive contained in the working layer is diamond. Particularly preferably, the hard materials released from the first material of the rotor disk are so soft (SiO ₂ , CeO ₂ ) or their grain size is so small (Al ₂ O ₃ , SiC, ZrO ₂ ) that they reduce the roughness and damage depth of the semiconductor wafer surface, which is determined by the processing by the abrasives from the working layer, do not increase.

In The rule is the degree of interaction between rotor disk and working shift for the two working shifts differ. This is for example the weight of the carrier, which leads to an increased interaction with the lower working layer leads, or at the distribution of the working gap supplied Operating equipment (cooling lubrication), which is on top and bottom produces a different coolant lubricant film. In particular, in a non-inventive, the sharpness of the working shift reducing rotor disc there is a strong asymmetric dulling between upper and lower working shift. That causes a different one Removal of the front and back of the semiconductor wafer, and undesirable roughness-induced deformation occurs of the semiconductor wafer.

13 shows, by way of example, the warp W of a semiconductor wafer which has been processed with an inventive carrier wafer made of PVC ( 55 ) and as a comparative example, the warp of a semiconductor wafer processed with a non-inventive carrier ( 54 ). The non-inventive rotor is in the example shown from stainless steel. Carbon of the working layer diamond dissolves in the stainless steel, the diamond becomes brittle and the working layer becomes dull. Due to the weight of the carrier disc, the interaction of the carrier disc with the lower working layer is greater than that with the upper one, so that the lower working layer becomes dull faster. As a result, an extremely asymmetrical material removal from the semiconductor wafer takes place between the lower and upper sides, with greatly different front and rear roughnesses. It forms a warp (strain-induced warpage). The warp is plotted against the radial measuring position R on the semiconductor wafer. The warp W denotes the maximum of the deflection of a force-free mounted semiconductor wafer due to deformation or strain over its entire diameter. The warp of the semiconductor wafer processed according to the invention is 7 .mu.m, that of the 56 .mu.m not processed according to the invention.

14 shows as an example the damage depths (sub-surface damage, SSD) of the lower (O) and upper side (U) of a semiconductor wafer (PVC film laminated to a stainless steel core) processed with a carrier according to the invention ( 58 ) and as a comparative example of a non-inventive carrier (glass fiber reinforced epoxy resin) machined ( 59 ). In the case of the semiconductor wafer processed according to the invention 58 the SSD is the same for both sides as part of the measurement error. In the semiconductor wafer not processed according to the invention 59 For example, the SSD of the side O machined by the upper working layer is significantly lower and that of the side U processed by the lower working layer is significantly higher than that obtained for both sides of the semiconductor wafer processed according to the invention. The SSD was determined using a laser-acoustic measuring method (measurement of the sound dispersion after laser pulse excitation).

15 shows, as an example, the RMS roughnesses RMS of the upper (O) and underside (U) of a semiconductor wafer processed with a rotor disk according to the invention (PVC on stainless steel) ( 58 ) and as a comparative example of a with a non-inventive rotor (glass fiber reinforced epoxy) machined ( 59 ). In the case of the semiconductor wafer processed according to the invention ( 58 ), the roughness is the same for both sides as part of the measurement error. In the semiconductor wafer not processed according to the invention 59 For example, the roughness of the side O machined by the upper working layer is significantly lower and that of the side U processed by the lower working layer is significantly higher than that obtained for both sides of the semiconductor wafer processed according to the invention. (RMS = root-mean-square, root mean square of the Rauhamplituden). The roughness was determined using a stylus profilometer (80 μm filter length).

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 10344602 A1 [0014, 0015]
• - US 6007407 [0014, 0054]
• - DE 10007390 A1 [0051]
• DE 102004040429 A1 [0057]
• - DE 19937784 A1 [0059]
• - DE 19954355 A1 [0060]
• EP 0208315 B1 [0113]

Claims (3)

A method for simultaneous double-sided grinding of a plurality of semiconductor wafers, wherein each semiconductor wafer is freely movable in a recess of one of a plurality of offset by means of a rolling device rotors and is thereby moved on a cycloidal trajectory, wherein the semiconductor wafers are machined between two rotating annular working discs material, wherein each working disk comprises a working layer containing bonded abrasive, characterized in that during processing the semiconductor wafers temporarily leave with a part of their surface the working gap delimited by the working layers, the maximum of the overflow in the radial direction being more than 0% and at most 20% is the diameter of the semiconductor wafer, wherein the overflow is defined as the measured relative to the working disks in the radial direction length to the one semiconductor wafer at a certain Zei point during grinding beyond the inner or outer edge of the working gap. Process according to claim 1, characterized characterized in that the semiconductor wafers at the temporary partial area Leaving the working gap gradually over the entire edge area the working shifts completely and essentially the same often paint over. Method according to one of the claims 1 or 2, characterized in that the semiconductor wafers the Work gap temporarily over the inner edge and temporarily over leave the outer edge of the working gap.